A process of separating aromatic compounds is to obtain para-xylene and benzene as main final products by processing a naphtha feedstock in a petrochemical plant. To obtain para-xylene, one of important products among aromatic compounds, a process of separating it from a xylene mixture has been commonly used. As examples of such process, there are processes using simulated moving bed adsorptive chromatography and crystallization caused by freezing point difference in each component, or a hybrid process which uses both processes together by connecting them serially, and the like.
In a process of separating aromatic compounds using a conventional simulated moving bed adsorptive chromatography as shown in FIG. 1, the simulated moving bed para-xylene separation process is only used as a process for separating para-xylene. Such process has some problems that there is limitation on increasing reformate production by inputting additional naphtha, due to the limited capacity of a simulated moving bed para-xylene separation process.
For complementing the problem, by noticing that para-xylene concentration in a xylene mixture from the product resulted from a selective toluene disproportionation process (STDP) nearly reaches to approximately 90 wt %, a hybrid process in which a crystallizer is attached to the selective toluene disproportionation process as represented in FIG. 2 have been developed. Owing to such system of dividing a para-xylene separation process, it became possible to increase reformate by additional naphtha input, or to improve para-xylene productivity by additional toluene input.